Do these tests:

1) gentle braking from 50-40 mph.

2) on the center lane of 3-lane highway (or equivalent so not leaning due to crown), make a gente s curve. You can stay in your lane.

On 1, if the test catches the problem you'll feel a crazy amount of steering shake.

On 2, you hold the wheel very gently (think pinch finger and thumb). If the test catches the problem, you'll get 2-3 gentle wiggles in the wheel when you cross past 0° on the steering wheel (feels like it's fighting you to go back the other way a couple gente tugs).

If either of those happen it's almost positively the rear control arms. (I've never figured out how to tell if it's just one I always replace both).

As to why at high elevation probably very similar to why mine that need replacing badly stopped being a problem. In my case i believe enough rust built up in the joint to make it tight.

In your case I'm thinking air bubbles in the grease change the dynamics of the joint as they change with air pressure.

(This is just educated guess).

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)